1. Field of the Invention
The present invention relates in general to anti-fuse programming circuits, and more particularly to an anti-fuse programming circuit which is capable of making an anti-fuse conductive in a dielectric breakdown manner to program it and verifying the programmed state of the anti-fuse.
2. Description of the Prior Art
A general fuse, when the amount of current exceeding a predetermined value flows therethrough, melts and blows due to a generated heat to form an open circuit for protection of the associated device.
On the other hand, a fuse is used in a redundancy circuit for a semiconductor memory device to replace a failed line with a spare line. In order to program the fuse used, there have been proposed various methods such as, for example, an electrical fuse method of applying an overcurrent to the fuse to melt and cut it and a laser cutting method of applying a laser beam to the fuse to burn and cut it.
Among the above methods, the laser cutting method is widely used because it is simple, reliable and easy to arrange. In this case, the fuse is made of a polysilicon wire or metal wire.
The overcurrent cutting methods requires a high current driver and fuse blowing pad, resulting in an increase in occupying area. Further, a residue may be present after the cutting, thus causing a switch-off phenomenon.
In the case of cutting polysilicon using a laser beam, an error may occur in accurately applying the laser beam to the polysilicon and a residue may be present after the cutting. In this case, the laser cutting method requires a large amount of processing time, and it is difficult and inaccurate to perform. Further, the repair is impossible at a package level, resulting in a degradation in reliability.
In order to solve the above problems, there has recently been proposed a new element, or a so-called anti-fuse, which can be programmed simply even at the package level.
The anti-fuse is programmed to interconnect an upper electrode and lower electrode. Namely, the anti-fuse includes an insulating film formed between the upper and lower electrodes in such a manner that it can easily be broken down according to a dielectric breakdown voltage which is a voltage difference between the upper and lower electrodes.
In this regard, the anti-fuse is programmed to interconnect two electrodes, whereas a general fuse is programmed to disconnect them from each other.
As a result, there is a need for a circuit which is capable of programming the anti-fuse and verifying the programmed result of the anti-fuse.